This invention relates to the handling of mixtures of chlorine-containing compounds and it is especially directed to high boiling products that invariably form during the Direct Syntheses of chlorosilanes. Such materials are called Direct Process Residue Wastes.
The Direct Process provides for the direct synthesis of monomeric chlorosilanes by the reaction of gaseous methyl chloride or hydrogen chloride with elemental silicon in a fluid bed reactor at an elevated temperature. This reaction is catalyzed and optimized to prepare dimethyldichlorosilane, by far the most important intermediate for the preparation of industrial "Silicones". The process is also optimized to prepare trichlorosilane, a very important intermediate to prepare transistor grade silicon and many organotrichloro-silane intermediates.
There is created in the Direct Process, a residue, which is obtained after distillation of the dimethyldichlorosilane and other chlorosilanes. This residue consists of a large number of by-products such as for example CH.sub.3 Cl.sub.2 SiSiCH.sub.3 Cl.sub.2, CH.sub.3 Cl.sub.2 SiSi(CH.sub.3).sub.2 Cl and other disilanes of the formula Si.sub.2 (CH.sub.3).sub.x Cl.sub.6-x wherein x equals either 1, 2, or 3, as well as trisilanes of the formula Si.sub.3 (CH.sub.3).sub.x Cl.sub.8-x, wherein x equals either 1, 2, 3, or 4, and minor amounts of disilylmethane structures such as CH.sub.3 Cl.sub.2 SiCH.sub.2 SiCH.sub.3 Cl.sub.2 and lesser amounts of disilylethane structures such as CH.sub.3 Cl.sub.2 SiCH.sub.2 CH.sub.2 SiCH.sub.3 Cl.sub.2 and small amounts of numerous organochlorosilanes of unproven structures. A typical high boiling residue from the methyl chloride direct process usually contains more than fifty percent by weight of chloride. A typical high boiling residue from the reaction with hydrogen chloride usually consists mostly of compounds of the type Cl(HSiCl).sub.x Cl wherein x=1,2,3, or 4, as well as SiCl.sub.4.
Many attempts have been made to utilize these residues as they are otherwise waste products and have to be subjected to various treatments to neutralize them and then they are landfilled which can create certain environmental problems. All attempts at utilizing certain of the distillable products from the residue have led to products which are expensive and are based on a source which is inconsistent at best and therefore is not desirable for large volumes of materials.
The first step of the instant process, the reaction of the alcohol with the chloride of the chlorine-containing silicon compounds has been described as a continuous process for the conversion of monomeric chlorosilanes to monomeric alkoxysilanes in U.S. Pat. No. 4,506,087 which issued Mar. 19, 1985 to Fischer, et al. Therein is described a complicated process and apparatus which has been found useful for such a process. This reference, however, does not describe the entire process set forth in the instant invention, and it does not set forth the fact that complex mixtures of materials, including polysilanes, can be converted to monomeric alkoxysilanes by the instant process.
The instant invention overcomes the problems set forth above and provides an economical process for obtaining valuable monomeric silane intermediates as well as valuable recovery of hydrogen chloride and hydrogen.